2.3.1 [Solid lattices] Flashcards
What are the 4 types of solid lattices?
Giant metallic lattices
Giant ionic lattices
Giant covalent lattices
Discrete (simple) molecular lattices
What is a Giant metallic lattice?
Metallic lattices are composed of a regular arrangement of positive metal ions surrounded by delocalised electrons.
What are the properties of Giant metallic lattices?
High melting and boiling temperatures
Good electrical conductivity
Good thermal conductivity
Malleability
Ductility
What are Giant ionic lattices?
Giant ionic lattices are composed of a regular arrangement of positive and negative ions. High melting and boiling point.
What are the properties of Giant ionic lattices?
High melting temperatures
Brittleness
Poor electrical conductivity when in solid but good when in molten
Often soluble in water
What are Giant covalent lattices?
Giant covalent lattices are called network covalent lattices. Consist of a giant network of atoms linked to each other by covalent bonds. Very strong very high melting point.
What are the most common giant covalent substances?
Diamond
Graphite
Graphene
Silicon oxide
What is diamond and what are its properties
Diamond is a macromolecular structure made up of carbon atoms forming 4 (sigma) bonds. Forms a giant three dimensional tetrahedral structure. (109.5 bond angle)
Extremely strong and hard because of the strong C-C bonding throughout the structure. Very high melting temperature because a great number of strong C-C bonds have to be broken in order to melt it. Large amount of heat energy required.
What is Graphite and what are its properties?
Graphite is a macromolecular structure made from Carbon atoms. Each carbon atom is bonded to 3 by (sigma) bonds, forming interlocking hexagonal rings, 4th electron on each carbon atom in a p orbital. Carbon atoms are close enough for the P orbitals to overlap producing cloud of delocalised electrons. Above and Below plane of rings. Electrons move freely allowing it to conduct electricity. Can be used in an electrode.
Graphite can be used as a lubricant, since there are weak IM/London forces between the layers they can easily slide over each other.
What are the properties of Graphite?
Good conductor of electricity as the delocalised electrons between the layers are free to move under an applied potential difference. Only conduct parallel to its layers. Metals can conduct in all directions
Act as a lubricant as a result of absorbed gases on the surface of the carbon atoms. not effective in vacuum.
What is Graphene and what are its properties?
Graphene is pure carbon in the form of a very thin sheet (2D) one atom thick. Carbon atoms are bonded in the same was as in graphite. Sheets are formed of hexagonal carbon rings very strong rigid material very lightweight. Has delocalised electrons move through each layer allowing it to conduct electricity
What are simple molecular structures?
Substances with simple covalent molecular structure consist of covalently bonded molecules held together by weak van der waals or intermolecular forces. Examples is structure formed by water. Held together by London forces. Molecules are held close tightly packed together
What are the properties of molecular solids?
Molecular solids in general have a low melting and boiling temperatures. In order to melt a molecular solid it is not necessary to break the covalent bonds within the molecules, Only necessary to overcome the intermolecular forces of attraction
Since intermolecular forces of attraction tend to be much weaker than covalent bonds little energy is required to break down the lattice structure of the solid and cause it to melt or vaporise.
London forces tend to increase with increasing number of electrons per molecule and also with increasing length of molecule. So longer molecules have higher boiling point.
